Control of atmospheric particles



United States Patent 3,534,906 CONTROL OF ATMOSPHERIC PARTICLES Jay DonGensler, Alexandria, Va., assignor to The Dow' Chemical Company,Midland, Mich., a corporation of Delaware No Drawing. Filed Nov. 20,1967, Ser. No. 684,550 Int. Cl. Atllg 15/00 US. Cl. 239-2 9 ClaimsABSTRACT OF THE DISCLOSURE This invention relates to a method for thecontrol of atmospheric moisture and more particularly relates to amethod for fog abatement and the modification of clouds.

In the past, many methods have been proposed to modify clouds to producerain or snow, to dissipate haze or fog, to modify and decrease theintensity of tropical storms or hurricanes, or to remove smoke, smog andthe like from the air. Most of the reported work in the area deals withcloud modification and many materials have been employed with varyingdegrees of success. In general, to produce rain from a cloud by seeding,it is necessary to employ an ice-former such as silver iodide or Dry Iceor a hygroscopic material such as NaCl, CaCl MgCl and the like. Usuallysuch seeding materials depend on a temperature within the cloud of lessthan 0 C. so that ice crystals form and grow. Many low clouds, fogs andthe like are too warm, however, and such seeding materials are notelfective. Attempts have been made to produce rain from low warm cloudsand fog by employing hygroscopic materials or sprays of water thereto toetfect coalescence and precipitation of the particles within the cloud.While rain has at times been produced by this method, such rainfall willnot propagate. itself unless the cloud was already in a metastablecondition. Another problem presented in present systems is that verythick layers of cloud or fog, e.g., 5000 ft., are normally required toachieve good nucleation, coagulation and precipitation. Therefore, whilea process to reliably control the agglomeration of atmospheric particlesis greatly de sired, no method has been heretofore provided which iseffective in producing the agglomeration and subsequent precipitation ofparticles suspended in the air, particularly when such particles areabove the freezing point.

It is an object of this invention to provide a means for controllingatmospheric particles by producing agglomeration and precipitationthereof. A further object is to provide a means whereby fog may bequickly and safely abated. A still further object is to provide animproved method for the modification of clouds to alter their physicalform and moisture content. A still further object is to provide a methodwhereby smoke, smog and the like may be substantially removed from theair thereby diminishing air pollution. These and other objects andadvantages of the present invention will become obvious from a readingof the following detailed description.

In accordance with the process of this invention, a polyelectrolyte infine particulate form is contacted with the fog, smoke, cloud or otheratmospheric mass of particles to be modified. The presence of thepolyelectrolyte ena'bles the water droplets or other particles in thefog, cloud or atmosphere to coalesce by altering the electrostaticcharge on such droplets. Such coalescence is therefore produced wtihoutdependence on the surrounding temperature thereof being below thefreezing point of water.

Suitable polyelectrolytes for use in the process of this invention maybe cationic, anionic, nonionic or amphoteric, hydrophobic or hydrophylicand include polyalkylenimines such as polyethylenimine orpolypropylenimine, polyalkylenepolyamines such as the condensationpolymers of diethylenetriamine and dihaloalkanes, sodium polystyrenesulfonate, copolymers of sodium acrylate and acrylamide, partiallyhydrolyzed, crosslinked, polyacrylamides such as are defined in US. Pat.3,247,171, ion exchange resins such as a condensation product ofepichlorohydrin and ammonia, polyalkylene oxides, copolymers of alkyleneoxides with other organic electrolytes, and the like. In order topossess the necessary properties for use in the process of thisinvention, the organic polyelectrolytes must have a molecular Weight ofat least 30,000 and preferably of at least 50,000. Such polyelectrolytesmay be employed either in aqueous solution, spray or mist form or in theform of a finely-divided particulate solid. In general, the mosteffective size of the particles of polyelectrolyte or polyelectrolytesolution is from about 10 microns to about 50 mesh (Standard sievesize). Particles smaller than 10 microns lose effectiveness in producingcoalescence of the atmospheric particles and particles larger than 50mesh, while effective, begin to significantly reduce the number ofparticles produced from a given volume of polyelectrolyte and thereforebecome ineificient.

Since the coagulation and precipitation of the water particles herein iselectrostatically produced, it is necessary that at least a portion ofthe polyelectrolyte employed contains a different charge from that ofthe fog or cloud to be treated. Therefore, since clouds and fogs usuallyhave an electronegative charge, it is often desirable to employ acationic electrolyte, or where the fog, cloud, or other particulate massto be coagulated and dispersed contains a positive charge, an anionicpolyelectrolyte may be employed. However, aggregation and precipitationof particles is also accomplished by the addition of a polyelectrolyteof similar charge but of different magnitude and which, therefore,disrupts the electrostatic equilibrium.

The amount of polyelectrolyte or polyelectrolyte solution required for agiven atmospheric condition will vary depending upon the density of theatmospheric particles, e.g., the density of the cloud or fog, the depthof the mass of atmospheric particles through which it is to pass, andthe like. As each polyelectrolyte particle passes through the mass ofatmospheric particles, differently charged particles combine to form aparticle of altered electrical charge which falls through theatmospheric mass, collides with other particles to produce a largeparticle and continues to increase in acceleration and speed until thesurface tension is overcome and the particle redivides. Each of thedivided particles then continues to fall and grow to produce achain-reaction of acceleration and division of particles.

Any suitable means may be employer to distribute the polyelectrolytewithin the fog, smoke, cloud, or other particle-containing atmosphericmass and thereby produce contact between the dissimilar particles, i.e.,the atmospheric particles and the polyelectrolyte particles. Forexample, spraying a solution of the polyelectrolyte above or within thefog or cloud from an airplane or helicopter, explosively dissiminatingthe polyelectrolyte within the cloud by means of a bomb or explodingrocket, spraying or blowing the polyelectrolyte from ground vehicles,and the like, produces sufiicient dispersion to cause coalescence andprecipitation of the particles and thereby produce dissipation of fog orsmoke and rain, snow or other precipitation from clouds.

The following examples are provided to more fully illustrate theinvention but are not to be construed as limiting to the scope thereof.

EXAMPLE 1 Steam was injected into a room 20 ft. x 12 ft. x 8 ft. until adense fog was produced. The degree of fog density was measured byshining a light a distance of 16 feet through the fog and into a lightintensity meter such that higher readings are produced on the lightintensity with less dense fog and lower readings with more dense fog. Areading of 120 units is achieved when no fog is present.

When the light intensity meter reading stabilized at 18 units, a 10weight percent aqueous solution of polyethylenimine (having a molecularweight of about 100,000) was sprayed as a fine mist about 4 feet abovethe beam of light for 10 seconds at the rate of 1 gm. of spray persecond. The spray was produced from a Quick-Fill spray bomb powered by Ccartridges which was moved back and forth between the light source andthe light meter. Within 30 seconds after spraying was started, the lightintensity meter showed a reading of 21 units and continued to show areading of 21 units for a total of two minutes. After a total of fiveminutes, the fog had returned to the equilibrium value of 18 units. Itshould be noted that the substantial reduction in fog is produced withan effective particle fall distance of only four feet.

In a control run, a spray of water was employed in place of the spray ofpolyethylenimine solution. During the ten second period of spraying, thelight intensity meter reading decreased to 16 units and remained at thislevel for about 45 seconds. After a total time of about five minutesfrom the beginning of the water spraying, the light intensity meterreading returned to the equilibrium value of 18 units.

EXAMPLE 2 In the same manner as Example 1, a weight percent solution ofpolyethylenpolyamine (Purifloc C-31) having a molecular weight of about100,000 was sprayed four feet above the beam of light for a period offive seconds at a rate of one gram of spray per second. After 30 secondsfrom the beginning of application of the spray, the light intensitymeter reading had increased to 20 units and remained at this value for aperiod of one minute. After a total of three minutes, the intensitymeter reading had returned to the equilibrium value of 18 units.

EXAMPLE 3 In the manner of Example 1, a weight percent aqueous solutionof polyethylenimine having a molecular weight of about 100,000 wassprayed for two minutes along a line four feet above the light beam.During this period the light intensity meter reading rose to a value of24 units and an additional three minutes was required for the reading toreturn to the equilibrium value of 18.

When a five weight percent solution of polyethylenepolyamine having amolecular weight of about 100,000 was employed in the same manner, thelight intensity meter reading increased to a value of 22 units and anadditional two and one-half minutes was required for the reading toreturn to an equilibrium value of 18 units.

Similar results are obtained when a fine (about 200 mesh) powdered formof a water-swellable, partially hydrolyzed acrylamide polymer containingabout 30% by weight sodium acrylate groups and crosslinked with about1500 ppm. of methylene bisacrylamide is dispersed into the steam in theplace of the polyethylenimine or polyalkylenepolyamine.

Likewise, similar results are obtained when a finely divided form ofsodium polystyrene sulfonate is employed in the place of thepolyethylenimine employed above.

In a control experiment employing water in the place of an aqueoussolution of polyethylenimine of polyalkylenepolyamine, the lightintensity meter reading decreased to 15 units during the spraying stepthen increased slowly to the equilibrium value of 18 units in aboutthree minutes.

EXAMPLE 4 In order to demonstrate the applicability of the process ofthis invention to disperse a warm fog from airport runways under actualfield conditions, an experiment was conducted at a large airport in thesouthern United States. For purposes of the test both a transmissometerand ground observers were employed to determine the effect of the teston visibility. The test was begun at 7:05 am. with an initial visibilityof feet to feet with no runway lights visible to the observers. Anaircraft was flown over one runway at an altitude of about 500 feet anda 5% solution of polyethylenimine having a molecular weight of about100,000 was applied at the rate of 200 lbs./ sq. mile in seven passesover the runway. Both transmissometer readings and ground visualobservers recorded that visibility rapidly increased with each pass ofthe spraying operation and by 8:00 am. after six of the seven passes hadbeen completed, visibility had increase to 3200 feet.

EXAMPLE 5 A heavily forested area covered by a large cloud of ascendingwhite-grey smoke from burning saw mill waste was treated with a 5 weightpercent aqueous solution of polyethylenimine by spraying a mist of suchsolution from an airplane just above the smoke (an altitude of about 100feet). As the polyelectrolyte solution passed into the smoke a definitecolor change to blue was observed, showing densification of the smakeand the color change and densification could be seen continuing downthrough the rising smoke. After a second application of polyelectrolyte,the forest could be seen through the treated portion of the smoke butwas not visibile through the untreated portions.

In a like manner, spraying from aircraft into moistureladen cloudcolumns of several thousand feet in height with aqueous solutionscontaining 1 to 10 weight percent polyethylenimine and using adeployment rate of from about 5.0 to 20.0 lbs. of solution per squaremile near the top of the clouds results in precipitation of asubstantial portion of such clouds in the form of rain. Similar resultsare achieved when other polyalkylenimines, polyalkylenepolyamines,copolymers of sodium acrylate and acrylamide are employed in place ofthe polyethylenlmme.

Various modifications can be made in the present invention withoutdeparting from the spirit or scope thereof for it is understood that Ilimit my self only as defined in the appended claims.

I claim:

1. A process for the control of particles suspended in the atmospherewhich comprises contacting a mass of suspended atmospheric particleswith an organic polyelectrolyte having a molecular weight of at least30,000 in fine particulate form to modify the electrical charge of saidatmospheric particles thereby to produce coalescence and precipitationof such particles.

2. The process according to claim 1 wherein the size of thepolyelectrolyte particles is between about 10 microns and about 50 mesh.

3. The process according to claim 1 wherein the molecular weight of thepolyelectrolyte is at least 50,000.

4. The process according to claim 1 wherein the polyelectrolyte is apolyalkylenimine.

5. The process according to claim 1 wherein the polyelectrolyte is apolyalkylenimine.

6 References Cited UNITED STATES PATENTS 2,835,530 5/1958 Schneider239-2 5 2,962,450 11/1960 Elod et a1. 239-14 X ROBERT B. REEVES, PrimaryExaminer U.S. Cl. X.R.

